LaunchBar is an award winning productivity utility that provides instant access to your applications, documents, contacts and bookmarks, to your iTunes library, to search engines and more, just by entering short abbreviations of the searched item's name.

DragThing is the original dock designed to tidy up your Macintosh desktop.

ASM brings back the application switcher menu (and more) to Mac OS X.

As close to nirvana as a todolist is likely to reach, especially when you throw in the iPhone app and the Gmail plugin. If you use multiple Gmail accounts, you'll need my userscript: http://userscripts.org/scripts/show/38389